Method and apparatus for sifting out fine particles by utilizing supersonic vibration

ABSTRACT

Method and apparatus for sifting out fine particles according to their original sizes, into which apparently larger-sized particles formed by the cohesion of such fine particles have been split by applying supersonic vibration in the solution, such sifting-out being carried out by applying supersonic vibration also to a set of the sieves of one or more mesh sizes.

United States Patent [1 1 Kammori et al.

[ METHOD AND APPARATUS FOR SIFTING OUT FINE PARTICLES BY UTILIZINGSUPERSONIC VIBRATION [75] Inventors: Ohiko Kammori; Isamu Taguchi,

Kawasaki City, Kanagawa Prefecture, Japan [73] Assignee: Nippon SteelCorporation, Tokyo,

Japan 22 Filed: Aug. 9, 1971 21 Appl.No.: 170,242

Related US. Application Data [63] Continuation-in-part of Ser. No.815,983, April 14,

1969, abandoned.

[30] Foreign Application Priority Data 209/233, 3, 5, 1, 269, 317, 319,379, 380, 364, 365; 210/19; 73/432 PS; 259/DIG. 43

1451 Sept. 4, 1973 [56] References Cited UNITED STATES PATENTS 3,490,584l/l970 Balamuth 209/1 2,785,768 3/1957 Ganchard 55/103 X 3,305,4812/1967 Peterson 209/233 UX 3,366,234 1/1968 Suhm et a1.... 209/213,463,321 8/1969 Vanlngen 209/233 X 3,472,202 10/1969 Webb 209/1 X OTHERPUBLICATIONS Allen-Bradley Sonic Sifter, l 1-4-65, pp. 2-8. 1 l465,

The Profitable Use of Testing Sieves, W. S. Tyler C0., Cleveland, Ohio;9-24-1940; pp. 20-21 Primary ExaminerTim R. Miles AssistantExaminerWilliam Cuchlinski, Jr. Att0rney-E. F. Wenderoth et a1.

[57] ABSTRACT Method and apparatus for sifting out fine particlesaccording to their original sizes, into which apparently larger-sizedparticles formed by the cohesion of such fine particles have been splitby applying supersonic vibration in the solution, such sifting-out beingcarried out by applying supersonic vibration also to a set of the sievesof one or more mesh sizes.

6 Claims, 12 Drawing Figures PATENTEDSEP 4191a SHEH 1 OF 2 FIG. 3

FIG. 2

FIG.

Attorneys FIG. 5 25 26*Y* METHOD AND APPARATUS FOR SIFTING OUT FINEPARTICLES BY UTILIZING SUPERSONIC VIBRATION This application is acontinuation-in-part of Ser. No. 815,983 filed Apr. 14, 1969 nowabandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates in general to a method and apparatus for sifting outfine particles, and more particularly to a method and apparatus forsifting out fine particles by utilizing supersonic vibration.

2. Description of the Prior Art A conventional and widely used methodfor sifting out fine particles such as powder of metal oxides, is themethod using a sieve having a comparatively rough mesh size of more thanabout 0.04 mm, while applying mechanical vibration to the sieve. Thismethod, however, is inefficient because as the mesh of the sieve becomesfiner, it gets choked up, and such choing can not be avoided even byapplying mechanical vibration, making it difficult to achieve goodsifting-out. In order to overcome this difficulty, when sifting out fineparticles in a solution by using a sieve having a fine mesh, there isused such a step as pressing from the top of the solution or, reversely,applying suction from the bottom of the sieve to reduce pressure, so asto raise efficiency. Even with such steps, the above method is notsuccessful in achieving efficient sifting-out, because fine particlestend to cohere to form what appear to be larger-sized particles, whichwillnot be completely separated into fine particles even when such adispersing agent as a surface activating agent is added and whichlarger-sized masses of particles tend to choke up the sieve and thereisthus great difficulty in sifting out particles according to variousgranular sizes.

In carrying out the conventional methods as described above metalfilters of fine mesh in the form of metal or a net made of fine steelwire are generally used. However, it is difficult to obtain such a nethaving a mesh size less than about 0.04 mm.

Regarding the production of the metal filter, there is known a methodfor producing it by sintering metal powder. By this method it ispossible to obtain sufficient mechanical strength and as fine a meshsize as about 0.01 mm, but the method is not successful in obtaining auniform size of mesh. Therefore, it is difficult to produce metalfilters having a uniform mesh and a mesh size less than 0.04 mm by theconventional metal filter production methods.

The above-mentioned difficulties in producing metal filters having amesh size less than 0.04 mm and in sifting out fine particles accuratelyaccording to the actual size even when using a sieve having acomparatively rough-mesh size of about 0.04 mm by the conventionalsifting-out methods, make accurate and efficient sifting-out of suchfine particles as powder of metal oxides extremely difficult.

SUMMARY OF THE INVENTION On the basis of studies to eliminate the abovedrawbacks from the conventional sifting-out methods, the inventors ofthe present invention have achieved a method for sifting out fineparticles accurately according to granular sizes after having separatedparticles which have cohered into larger-sized particles by utilizingsupersonic vibration, and also by applying such vibration to the sieveso as to prevent its choking and to obtain good sifting-out of fineparticles.

Supersonic vibration, has been used for the cohesion of such fineparticles as coal dust in water into largersized particles so as tofacilitate their precipitation to separation, for metal electrolysis tomake fine powder of metals, for the overcoming of the cohesion oforganic matters contained in a solution to make extremely fine particlesof such matters, and for cleaning the mechanism of a watch.

However, such uses of supersonic vibration have nothing to do with itsutilization according to the present invention for sifting-out of fineparticles according to their actual sizes and increasing the sifting-outspeed.

The principal object of the present invention is to provide a method ofwet-type sifting-out of fine particles and an apparatus therefor,according to which method, supersonic vibration is applied to fineparticles, so as to prevent cohesion of such particles, maintain them inthe well dispersed state, and also to prevent choking of the sieve,thereby making possible rapid and efficient sifting-out of particles ofa mesh size less than 0.04 mm.

Another object of the present invention is to provide a method ofwet-type sifting-out of fine particles and an apparatus therefor, bywhich are made possible an increase of the sifting-out speed of fineparticles and rapid and accurate sifting-out of various kinds of powderaccording to actual granular sizes.

In order to attain the above objects, the present invention ischaracterized by sifting out fine particles rapidly in a solution,applying supersonic vibration to one or more kinds of sieves of finemesh and also to apparently larger-sized particles formed by thecohesion of fine particles, so as to separate them into original sizes.That is to say, the present invention comprises a method according towhich supersonic vibration is applied to a solution made by placing theto-be-siftedout fine particles into water, alcohol or other liquids inwhich such particles are insoluble, to divide apparently larger-sizedparticles formed by the cohesion of such fine particles into originalsizes of the fine particles; sieves of one or several different meshsizes are used in a number of stages to sift out the fine particlesaccording to granular sizes; supersonic vibration is applied to theseparation zone to vibrate the sieve, so as to prevent chocking of thesieve and accelerate siftingout; and if necessary, sifting-out isaccelerated by suction; all these features being for achieving anefficient sifting-out of fine particles.

Furthermore, the above described object of the present invention can beattained by providing an apparatus comprising a continer adapted toreceive a liquid in which fine particles are suspended, a fine sievemeans fitted to the container to assume an adequate position and asupersonic transmitter inserted in the container, said apparatus beingcharacterized in that the said fine sieve means comprises preferably aplurality of metal filters each having multiple mesh openings of a fixedsize in a fixed plane and superposed in closely spaced steps, the tipportion of said supersonic transmitter being in the form of a truncatedcone having an end surface larger than the effective plane of said metalfilters and positioned near the uppermost filter surface. The apparatusis further characterized in that the said container is divided into anupper and a lower portion,

the filter is interposed between both container portions, and the lowerend of the upper container portion has an inner diameter smaller thanthe effective diameter of the filter while the upper and of the lowercontainer portion has an inner diameter larger than the effectivediameter of the filter.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-section of oneembodiment of the apparatus according to the present invention forsifting-out fine particles by applying Supersonic vibration.

FIG. 2 is a cross section of another embodiment of the apparatusaccording to the present invention.

FIG. 3 is a cross-section of the main part of the structure of theapparatus shown in FIG. 2.

FIG. 4 is a cross-section of one embodiment of the sieve of fine meshused in the apparatus according to the present invention.

FIG. 5 is a enlarged cross-section of part of the metal filter base usedas starting material for the metal filter for the apparatus according tothe present invention.

FIG. 6 is a enlarged cross-section of part of the metal filter producedfrom the base shown in FIG. 5.

FIG. 7 is a cross-section of one embodiment of the holder of the sieveused for the apparatus according to the present invention.

FIG. 8 (A), (B), (C), (D) and (E) are microphotographs of powderyvanadium carbide subjected to sizing by the apparatus of the presentinvention and shown fine particles of more than 20 u, 20-l 5 1., -10 u,10-5 1., and not more than 5 g, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENT One embodiment of the apparatusaccording to the present invention shown in FIG. 1, comprises mainly ahorn-type supersonic oscillator I connected at its upper part with asupersonic wave generator, several cylindrical sieve supporting frames 2placed one on another (for example, having dimentions of 35 mm insidedia., 44 mm outside dia. and mm height), the sieves 3, 4 and 5 havingdifferent mesh sizes getting finer from the top down and beingpositioned between the frames 2. A line 6 leads from the supersonic wavegenerator to the oscillator l, and the vibration transmitter 7 ismounted on the tip of the supersonic oscillator l. A funnel 8 isprovided beneath the lowermost sieve 5 and a suction pipe 9 connectedwith a suction pump opens into the space around the funnel 8. Atransmitting medium 10 is provided around the oscillator 1.

According to the present invention, the application, as shown in FIG. 1,of supersonic vibrations directly to the sieve 3 from the vibrationtransmitter 7 for transmitting supersonic vibrations which is placedclose (about 0.5 cm) to the sieve 3 in the transmitting medium in theliquid state, together with the reflection of supersonic vibrations fromthe sieve 3, 4, etc., is effective in dispersing supersonic waves.

The present invention is characterized by using metal filters having alarge number of mesh openings of a definite size in a fixed plane, asthe aforesaid fine sieves 3, 4, etc. in the sieving apparatusconstructed as described above. In order to prepare such a metal filteras used in the present invention to sift out fine particles, a thinmetal or organic filter having a fixed mesh size is used as a startingmaterial. The material is plated with nickel or platinum so as to have apredetermined fine mesh size. The metal filter thus produced serves topartly reflect the supersonic energy transmitted thereto, by virtue ofits metallic character, and the reflected supersonic energy is againreflected by the lower end surface of the supersonic transmitter. Suchultrasonic propagation is effective for perfect dispersion of fineparticles between the transmitter and the filter. An experimentconducted by the present inventors for comparison between such a metalfilter as described above and a typical marketed organic filter of thesame mesh size proved that the metal filter is markedly higher in thespeed and accuracy of sieving. It is possible to subject fine particlesto a grain size distribution test or sizing, by superposing a number ofmetal filters having different mesh sizes one above another asillustrated.

One of the sieves 30 composing the said sifting-out device is shown inFIG. 4 (in contrast to the sieves 3 to 5 shown in FIG. 1). This sieve 30is formed by securing a metal filter 32 having a mesh size as fine asl-50 p. in a ring 31 made of an elastic and corrosion resistant materialsuch as ethylene tetrafluoride. In addition to ethylene tetrafluoride,there can be used as the material of the ring, acrylic resin, polyvinylchloride, polyethylene and other synthetic resins and rubber; which arecorrosion resistant and which can be substituted one for anotherdepending on the kind of suspension. It is preferred that these ringshave the same shape so that they can be interchanged and also have ashape such as to be water-tight where they abut one another.

The metal filter 32 having a mesh size as fine as l-50 p. is generallymade by plating a metal film having many fine holes of uniform size withnickel and then with platinum to uniformly reduce the size of the holes.This filter is attached to the back of the ring 31 as described above orto an appropriate part of the ring 31 by an appropriate method, to formthe sieve 30.

A description will now be given of the metal filter having a fine meshused for the apparatuses according to the present invention. The metalfilter is made from a metal film having many holes of a certain constantsize. The film is subjected to electroplating, so as to reduce the sizeof the holes and to improve the mechanical strength and corrosionresistance. However, when using a metal film having too large a holesize to begin with, there can be produced only a metal filter having apoor quality having a small hole opening ratio and a low sifting-outefiiciency. When electro-plating conditions are not proper, the holesize of the metal filter becomes non-uniform and it is impossible toproduce filters of uniform hole size. It is, therefore, recommended touse, as a starting material, a metal film having many holes of aconstant size less than 50 u.

The following is an explanation of the filter production methodaccording to the present invention, using examples:

A nickel film (IO-2O u thick: about 30 p. in mesh size) and havingdimentions of 55 X 55 mm having many holes of constant, fine size madeby photographic and electrolytic etching, was immersed in dilutehydrochloric acid for about 10 minutes to remove the surface layer, wasrinsed with water, and immersed in and rinsed with methanol whileapplying supersonic vibrations at a frequency of about 40 KC. Afterbeing taken out of the solution and dried, it was placed between twobrass plates 60 X 60 mm and 2.5 mm thick having, at their center, a holeof 45 mm dia. This combination was painted with an insulator except forthe said metal film,

and dried. Being held hold in this way, the combination was immersed inan electro-plating bath, to be subjected to nickel plating using thefilm as a cathode and a nickel plate as an anode, under the followingconditions:

The progress of plating was observed through an optical microscope fromtime to time; the operation was stopped when the holes were reduced to 2larger than the desired hole size. After being completely rinsed withwater, the nickel-plated metal film was subjected to platinum platingusing itself as a cathode and a platinum plate as an anode, under thefollowing conditions:

Electrolytic current density: l-5 mA/cm Volume of plating bath: 1000 mlTemperature of plating bath: about 70"C pH of plating bath: about 6.5Composition of plating bath:

Platinic chloride (hexahydrate); l3 gll Monoammonium phosphate: 45 gllDiammonium phosphate: 240 gll The progress of plating was observedthrough an optical microscope from time to time; the operation wasstopped when the desired hole size was obtained. After being rinsed withwater, the platinum-plated metal film was rinsed with methanol anddried.

By using this method, it is made possible to produce metal filtershaving holes of any uniform size between 1 and t. Such metal filtershave high mechanical strength and excellent corrosion resistance andtherefore, they can to be used in filtration and other treatments offine particles.

- For use in the sifting-out of particles for which high corrosionresistance is not required, the single layer of nickel is enough, andadditional platinum plating can be omitted. The use of nickel andplatinum for metal electro-plating makes it possible to reduce the holesize uniformly, but, for the metal electro-plating method according tothe present invention there can be used copper or such other metals asare used for electro-plating of the normal type, as well as nickel andplatinum used in the Example above.

FIGS. 5 and 6 illustrate the metal filter produced by the method of thepresent invention.

In the figures, the metal film 25, should be less than 20 ;1.,preferably about 5-10 p, in thickness (T). The material of the metalfilm 25 is selected from among nickel, copper, iron, zinc, aluminum,chromium, silver, platinum, molybdenum, tungsten, silicon, germanium,etc. and their alloys, preferably nickel and copper. This metal film isso processed that many holes 26 of constant, fine size are made by achemical or electrochemical method, with a predetermined distance fromthe edge of a hole to that of another (hereinafter referred to as thedistance between holes) (Y) of less than 20 pi. The shape of the hole 26made in the metal film 25 is generally square, or round, if required.The size (W) of the hole 26 (meaning the diameter if the hole is round)is required to be less than about t, such size being convenient for thereduction of the size by the deposit of a metal layer. The reasontherefor is as shown in FIG. 6 that the specifications of the metal film25 are determined according to the desired distance between holes 27 ofthe finished metal filter 34. If one half of the difference between thesize of hole (W) in the metal film and the size of the reduced hole (W')in the metal filter 34, on which the metal layer has been despoited,that is, the thickness (X) of the metal layer deposited on the metalfilm, becomes too great, the size (W') of the reduced hole of the metalfilter varies widely. The thickness of the metal layer deposited on themetal film is preferably less than 15 ,u. As described below, when thesize of the reduced hole of the metal filter is desired to be 35-] u,the size of hole (W) on said metal film should be less than about 50 u.

The material of the metal layer 28 is a metal selected from amongnickel, copper, tin, chromium, zinc, cadmium, gold, silver, platinum,etc. and their alloys according to uses of the metal filter, taking intoconsideration their mechanical strength and resistance to corrosion bysolvents required for such uses.

Depending on the use, either a single layer or multilayer deposit ofmetal can be used. For depositing the metal layer on the metal filmelectroplating, chemical plating or other suitable methods can be used.Among these electro-plating is most-preferred, because it ensuresoverall coverage of the metal film with a metal layer, uniformity of thethickness of the layer and control to the desired thickness.

In anticipation of the application of supersonic vibrations the size ofthe hole (W') and the distance between holes (Y') of the metal filter 34should be maintained respectively between about 35 and l p. and betweenabout 20 and 50 u respectively while retaining the required hole openingratio of 0.22O percent.

Referring to the method of producing a metal filter of finer hole sizethan the above described, that is, less than I ;1., such a metal filtercan also be made by plating an organic filter base, thereby reducing thesize of holes uniformly and making the filter rigid and corrosionresistant.

For plating said organic filter base with metal there can be used anyknown method, but in order to obtain good uniform hole size, the use ofsupersonic vibration during plating is recommended. Among various knownmethods for plating, one of those which is suited for the above purposeand by which good results can be obtained, is the three-staged platingmethod according to which are carried out firstly, a non-electrolytic(chemical) plating of an organic base with nickel, secondly,electro-plating with nickel, and thirdly, electro-plating with paltinum.Particularly, the plating with platinum is necessary to improvemechanical strength and corrosion resistance.

The application of supersonic vibration is useful in plating the metalfilm as well as in plating the organic filter base, as mentioned above.It is recommended that while being held in an appropriate state, a metalfilm having many holes of constant, fine size be immersed in athreatment bath, and the electro-plating carried out, using the film asthccathode, with the application of supersonic vibrations, so as toreduce uniformly the holes. By this method good results can be obtained,and

a three-stage metal layer is deposited on the film.

In using a metal filter having holes of fine size for the sifting-outaccording to the present invention, there are shown in FIG. 4. As shownin the figure, the holder 33 is made of a rigid, flexible, chemicalcorrosion resistant synthetic resin such as ethylene tetrafluoride,having a groove 37 on the inside surface between a concave part 35 onthe top surface and a convex part 36 on the bottom surface, such groove37 being so constructed as to receive the metal filter 34. A cut 38 isprovided in the holder 33 for enabling it to be spread to receive themetal filter. The use of such a holder facilitates the fixing of themetal filter and accelerates the sifting-out speed, further raising theaccuracy of measurement.

Briefly the sifting-out method according to the present invention, usingthe apparatus shown in FIG. 1 comprises placing a liquid such asmethanol in the cylindrical supporting frames 2, moving the vibrationtransmitter 7 in the tip of the horn-type supersonic oscillator 1 toabout 0.5 cm above the sieve 3 having an appropriate mesh size andapplying supersonic vibration to the sieve. There is fed into thecylindrical supporting frame 2 a sample in the form of a methanolsolution in which the to-be-sifted-out powder has been dispersed bysupersonic vibration, and supersonic vibration is applied to sift thepowder out in the frame 2. In this case, if necessary, suction isapplied through the suction pipe 9. When using a number of sieves inmultistages, uppermost sieve 3 is removed and rinsed with methanol afterthe above operation is finished, and then the vibration transmitter 7 ismoved to about 0.5 cm above the next sieve 4 and the same operation asdescribed above is repeated. Thus, particles are sifted out bysuccessive use of the sieves 3, 4 and 5 according to different granularsizes.

FIG. 2 shows another embodiment of the apparatus according to thepresent invention.

The apparatus shown in FIG. 2 includes a supersonic vibrator 11 and asupersonic transmitter 17 fitted thereto. The vibrator 11 is connectedto a supersonic generator (not shown) through a cord 16. A container inthe form of a funnel is divided into an upper portion 12 and a lower one18. The upper funnel portion 12 receives the transmitter 17 and a liquidcontaining fine particles to be sifted out. Fine sieves 13 areinterposed between these two funnel portions 12 and 18. The sieves 13are superposed and fastened by clamp means 20. A suction bottle 21 isconnected with the lower funnel portion 18 and has a port 19 connectedthrough a pipe to a pump for pressure reduction. A tube 22 is placed inthe bottle 21 to collect the liquid flowing down from the lower funnelportion 18.

Referring now to FIG. 3, the tip portion of the supersonic transmitter11 is in the shape ofa truncated cone. The plane end surface of thetransmitter l 1 has a diameter 1 larger than the diameterfof theeffective circular area of the filter 13 opposed to the transmitter endsurface, which is adjacent to the surface of the filter 13 and inparallel therewith. This arrangement constitutes a feature of thepresent invention. It should be noted here that the effective circulararea of the filter 13 refers to the part of the surface of the filter 13which part remians uncovered by a filter holder receiving thecircumferential annular portion of the filter 13. When it is placedbetween the two funnel poritons, the said part practically comes intocontact with the suspension, that is, the liquid in which fine particlesare suspended.

When the transmitter 11 having the truncatedconical tip portion isplaced in the suspension existing in the upper funnel portion 12, withthe tip surface located near the upper surface of the top filter 13, the

suspension surrounded by the plane end surface of the transmitter 11,the upper surface of the said filter 13 and the said wall of the upperfunnel portion 12 is in a nearly closed condition (which is not aperfectly closed condition so that the liquid and the fine particlessuspended therein flow through the narrow clearance between thetransmitter and the side wall of the upper funnel portion). Therefore,the fine particles suspended in the liquid thus narrowly enclosed can becompletely dispersed by supersonic vibration. Moreover, since thediameter 1 of the tip surface of the transmitter 11 is larger than thediameterfof the effective circular surface of the filter 13 opposed tothe transmitter end surface, and also since both of the abovementionedsurfaces are in spaced parallel relationship with each other, sufficientand uniform supersonic transmission to the surface of said filter 13 ispossible. This also contributes to perfect dispersion of fine particles.The reason for such concentrated supersonic transmission to the fineparticles just above the filter 13 is as follows: Even if the fineparticles are once uniformly dispersed in a much larger amount ofliquid, the fine particles existing at such places in the containerwhere no sufficiently effective supersonic vibration is appliedagglomerate immediately because of their cohesive property. Thus,perfect particle dispersion is difficult, and much supersonic energy iswasted. With this fact in mind it is contemplated in the presentinvention to apply supersonic vibration only to the fine particles justabove the filter 13, whereby the fine particles just about to be siftedout by the filter are perfectly dispersed. Also, no more dispersion thannecessary takes place. This is extremely advantageous in terms ofoperating efficiency. In addition, according to the present invention,fine particles suspended in a liquid are sieved while supersonictransmission is performed; therefore, the sieves (filters) will not getclogged.

When superposing different metal filters 13 according to our invention,it is effective to place them in such a way that the higher the filterposition the larger the mesh size, and also to space the filters 13closely, the preferable spacing being less than 2 mm. This is due to thefact that there occurs effective supersonic transmission even to thelowermost filter and that, because of the close spacing of the filters,the suspension fills the space between the filters continuously bycapillarity. The suspension is the supersonic transmitting medium.Therefore, if the space between the filters is continuously filled withthe suspension, there occurs desirable ultrasonic transmission even tothe fine particles over the lowermost filter, so that the sizing orgrading accuracy is improved. It is not preferable for the filterspacing to exceed 2 mm because the suspension becomes discontinuous.

Furthermore, in the present invention it is convenient in respect ofgrading to make the sizes of the upper and lower funnel portions 12 and18 and the filters 13 as required, in such a way that, as shown in FIG.3, the inner diameter s of the lower end of the upper funnel portion 12is smaller than the diameterfof the effective circular area of thefilters 13 while the inside diameter s of the upper end of the lowerfunnel portion 18 is larger than the said diameter f of the filters 13.By doing this, it is possible to prevent fine particles from enteringbetween the bottom surface of the upper funnel portion 12 and the filterholder and between the top surface of the lower funnel portion 18 andthe filter holder during a sizing operation.

As illustrated and aforementioned, the liquid collecting tube 22 islocated below the lower funnel portion 18. This serves to collect fineparticles which are smaller than the mesh size of the lowermost filter13. The fine particles received by this tube are, as required, separatedfrom the liquid by means of a common organic filter and subjected toweight measurement and analysis. The tube 22 should be spaced from arubber plug fitted to the top of the suction bottle so that the pressurereduction through the port 19 is effective.

An adequate supersonic frequency employed in the apparatus of thepresent invention is on the order of -100 KC. The supersonic transmmiteris made preferably of a material which has excellent corrosionresistance such as stainless steel. The vertical shift of thetransmitter to a predetermined position is conducted by a handleoperation.

As mentioned above, the method of the present invention makes possiblenot only separating the particles cohered into apparently larger-sizedparticles into original sizes of fine particles but also sifting-out offine particles according to granular sizes and aquisition of particlesof desired granular size. Such sifting-out is rapid and efficient, andcan be carried out without choking of the sieves, making possibleoperation for a long time without replacement or cleaning of the sieves.

The method of the present invention is devised for universality in use,so that it can be applied to wet-type sifting-out of and granular testson fine powder, foreshadowing the possibility of manufacture ofapparatuses for these purposes. Moreover, it is anticipated that thefiltration speed for removing fine particles from solution could begreatly raised by use of the method of the present invention, ascompared with those obtained when using various filters in theconventional manner. Therefore, it is expected that the application ofthe method of the present invention will be highly effective, forinstance, in the removal of yeast from draught beer, the separation ofslime from pyrite containing precious metal and the recovery of raremetal during smelting.

Examples of the present invention will be described hereinafter.

Here follow examples, in which fine particles of vanadium carbide, anoxide inclusion residue extracted from steel, and a sulfide residueextracted from steel were subjected to sizing by using the apparatusshown in FIG. 2.

EXAMPLE 1 Under the following conditions, 100 mg of marketed syntheticvanadium carbide powder was submitted to sizing.

In this example, the apparatus shown in FIG. 2 was as follows:

Metal filters: four in number Size of mesh opening: 20 p, .4., 10 11., 5,1.

Space between filters: 1.5 mm

Diameter of the tip of the supersonic transmitter, 6

: 19 mm Diameter of the effective filter area,f 16 mm Diameter of thelower end of the upper funnel portion s 15.5 mm

Diameter of the upper end of the lower funnel portion 5' 16.5 mm

Distance between transmitter tip and topmost filter Supersonic frequency20 KC Liquid Methyl alcohol The sieving operation was as follows: First,methyl alcohol (5 ml) was supplied into the upper funnel portion, andsupersonic transmission was started. After methyl alcohol got into thelower funnel portion, the fine particles previously dispersed in methylalcohol (about 5 ml) by supersonic vibration were fed gradually into theupper funnel portion with a squirt. Sifting was continued while methylalcohol was replenished little by little. After the completion ofsieving, cleaning was done well with methyl alcohol. Then supersonictransmission was stopped, the transmitter was drawn out, and thepressure reducting pump was operated for suction for 2 or 3 minutes.Thereafter, the clamping means was removed and the filters were takenout together with the holders. The assembly of the filters and holderswere placed in a dryer, where the fine particles of vanadium carbidewere dried. The particles were then allowed to stand for cooling in adessicator and directly weighed. The weight of the fine particles oneach of the filters was ascertained from the weight of the metal filterand holder which had previously been weighed.

FIG. 8 (A), (B), (C), (D) and (E) are microphotographs showing theparticles of vanadium carbide on each of the filters, and correspond tothe grain sizes of more than 20 IL, 20-15 l5p.-l0 ;L, 10-5 1.1., and notmore than 5 ;1., respectively. As will be clear from the photographs,the grading result was very successful. In addition, Table 1 shows theweight ratio obtained for each grain size range. The operation wasrepeated five times to examine the reproducibility. As a result, it wasmade clear that the reproducibility was sufficiently excellent to standgood in actual practice. Besides, the average time required for thesizing was 15 minutes. This means that the grading operation was high inefficiency.

With the use of the aforesaid apparatus of the present invention, mg ofoxide inclusion residue extracted from steel was subjected to sizingunder the same conditions as in Example 1. While, in Example 1, theweight ratio for each of the particle size ranges was determined.Example 2 was directed to analysis of the composition of the particlesin each of the different grain size ranges. Based on the result of theanalysis, the content ratio of the components, that is, silicon oxide(Slo aluminum oxide (A1 0 ferrous oxide (FeO), manganese oxide (MnO),and chromium oxide (Cr O in each particle size range was obtained asseen in Table 2. The particle analysis was carried out in the followingmanner. The particles left on the metal filters taken out with theholders were put in a beaker containing methyl alcohol, and supersonicvibration was applied from below, with water used as its transmittingmedium, thereby separating the particles from the filters. Thereafter,the particles were submitted to filtration with the use ofa usualorganic filter (such as a German filter and a New clupore filter) andthen subjected to the intended analysis. In this example, the particlesThe aforesaid apparatus was used under the same operating conditions asin Example 1 to grade 50 mg of particles of a residue including sulfideswhich had been extracted from steel. Three different metal filters of 10l, 5 u and 3 across mesh openings were employed in this example. Aftercompleting the sizing, detection of compounds was carried out by themethod of X-ray diffraction analysis. The result is shown in Table 3.

Table 3 makes it clear that ferrous sulfide (FeS) and cementite (Fe C)coexisted in the extracted residue.

TABLE 3 Grain size t) Detected compound More than FeS 10-5 FeS 5-2 FegCNot more than 2 Fe,C (Not subjected to sizing, left intact) Fe,C

The method of the present invention for sifting out fine particles byusing supersonic vebration can also be applied to research on inclusionsand precipitates in metal samples. Supersonic vibration can also make itpossible to isolate the inclusions and precipitates from the samples,retaining the same forms as they are present in the samples andaccelerating the dissolution of the sample matrix with a dissolvingsolution such as iodine-method. Measurement of size distribution anddetermination after size classification of the inclusions andprecipitates can be carried out, using the inclusions and precipitatesresidues which have been isolated by the above-mentioned supersonicdissolution method and classified according to the name sizes as theyare present in the samples by the method of the present in- LII ventionof sifting out. The results are of much use in tests and research onmetal samples.

What we claim is:

1. An apparatus for sifting out fine particles by utilizing supersonicvibration, comprising:

a container adapted to receive a suspension containing fine particles tobe sifted out,

a sieve means fitted in the container, said sieve means comprising ametal filter having a multiplicity of mesh openings of a definite sizein a fixed plane, and

a supersonic transmitter having the shape of a truncated cone and placedin said container, the transmitter having a plane tip surface which islarger than the effective area of said metal filter and located near theupper surface of the filter in parallel therewith.

2. An apparatus as claimed in claim 1 wherein said sieve means comprisesa plurality of metal filters superposed in steps spaced sufficientlyclose for said suspension to fill the space between the filterscontinuously by capillarity.

3. An apparatus as claimed in claim 2 wherein the metal filter spacingdoes not exceed 2 mm.

4. An apparatus as claimed in claim 1 wherein said container is dividedinto an upper and a lower portion, the filter is interposed between saidcontainer portions, and the lower end of the upper container portion hasan inner diameter smaller than the effective diameter of the filterwhile the upper end of the lower container portion has an inner diameterlarger than the effective diameter of the filter.

5. A method of sifting out fine particles by utilizing supersonicvibration, which comprises;

preparing a suspension by mixing a powdery substance with a liquid inwhich the substance is insoluble,

placing the thus prepared suspension in a container having a siftingdevice therein with at least two filters superposed and spacedsufficiently closely to one another that said suspension fills the spacebetween said two filters spontaneously due to capillary action, and

placing a supersonic transmitter in said container near the uppersurface of the uppermost filter and operating said transmitter forimparting a supersonic vibration having a frequency of 10 to KC to thefilters through the suspension between the transmitter and the uppermostfilter and the suspension between the filters, whereby fine particlesare sifted from said suspension as it passes through the filters.

6. A method as claimed in claim 5 wherein said supersonic transmitter ispositioned about 0.5 cm above the upper surface of the sieve.

1. An apparatus for sifting out fine particles by utilizing supersonicvibration, comprising: a container adapted to receive a suspensioncontaining fine particles to be sifted out, a sieve means fitted in thecontainer, said sieve means comprising a metal filter having amultiplicity of mesh openings of a definite size in a fixed plane, and asupersonic transmitter having the shape of a truncated cone and placEdin said container, the transmitter having a plane tip surface which islarger than the effective area of said metal filter and located near theupper surface of the filter in parallel therewith.
 2. An apparatus asclaimed in claim 1 wherein said sieve means comprises a plurality ofmetal filters superposed in steps spaced sufficiently close for saidsuspension to fill the space between the filters continuously bycapillarity.
 3. An apparatus as claimed in claim 2 wherein the metalfilter spacing does not exceed 2 mm.
 4. An apparatus as claimed in claim1 wherein said container is divided into an upper and a lower portion,the filter is interposed between said container portions, and the lowerend of the upper container portion has an inner diameter smaller thanthe effective diameter of the filter while the upper end of the lowercontainer portion has an inner diameter larger than the effectivediameter of the filter.
 5. A method of sifting out fine particles byutilizing supersonic vibration, which comprises; preparing a suspensionby mixing a powdery substance with a liquid in which the substance isinsoluble, placing the thus prepared suspension in a container having asifting device therein with at least two filters superposed and spacedsufficiently closely to one another that said suspension fills the spacebetween said two filters spontaneously due to capillary action, andplacing a supersonic transmitter in said container near the uppersurface of the uppermost filter and operating said transmitter forimparting a supersonic vibration having a frequency of 10 to 100 KC tothe filters through the suspension between the transmitter and theuppermost filter and the suspension between the filters, whereby fineparticles are sifted from said suspension as it passes through thefilters.
 6. A method as claimed in claim 5 wherein said supersonictransmitter is positioned about 0.5 cm above the upper surface of thesieve.